SPST Relay Theory of Operation

The operation of the reed switch is based on the principle of magnetic induction. When a magnet, (permanent or electromagnetic) is in close proximity to an object comprised of soft iron, the object magnetizes.

As a strong magnetic field moves adjacent to the reed switch, the contacts become induced magnets and attract each other. The contacts then close and create a continuous electrical path throughout the switch.

When the magnetic field is removed, the contacts reopen. In processes requiring a higher current and power, the reed switch can be used to control a solenoid relay of the necessary rating. The limitations to this process are dependent upon the strength of the magnet and the overall reluctance of the magnetic circuit.

TRIAC Circuit Theory of Operation

When a magnet approaches a proximity switch, the reed switch inside the housing magnetizes. As a result, the contacts of the reed switch close and create a continuous electrical path through the TRIAC supporting the connected load. When the magnetic field is removed, the contacts reopen and discontinue the electrical path to the TRIAC.